ImportanceSARS-CoV-2 infection is associated with persistent, relapsing, or new symptoms or other health effects occurring after acute infection, termed postacute sequelae of SARS-CoV-2 infection (PASC), also known as long COVID. Characterizing PASC requires analysis of prospectively and uniformly collected data from diverse uninfected and infected individuals.ObjectiveTo develop a definition of PASC using self-reported symptoms and describe PASC frequencies across cohorts, vaccination status, and number of infections.Design, Setting, and ParticipantsProspective observational cohort study of adults with and without SARS-CoV-2 infection at 85 enrolling sites (hospitals, health centers, community organizations) located in 33 states plus Washington, DC, and Puerto Rico. Participants who were enrolled in the RECOVER adult cohort before April 10, 2023, completed a symptom survey 6 months or more after acute symptom onset or test date. Selection included population-based, volunteer, and convenience sampling.ExposureSARS-CoV-2 infection.Main Outcomes and MeasuresPASC and 44 participant-reported symptoms (with severity thresholds).ResultsA total of 9764 participants (89% SARS-CoV-2 infected; 71% female; 16% Hispanic/Latino; 15% non-Hispanic Black; median age, 47 years [IQR, 35-60]) met selection criteria. Adjusted odds ratios were 1.5 or greater (infected vs uninfected participants) for 37 symptoms. Symptoms contributing to PASC score included postexertional malaise, fatigue, brain fog, dizziness, gastrointestinal symptoms, palpitations, changes in sexual desire or capacity, loss of or change in smell or taste, thirst, chronic cough, chest pain, and abnormal movements. Among 2231 participants first infected on or after December 1, 2021, and enrolled within 30 days of infection, 224 (10% [95% CI, 8.8%-11%]) were PASC positive at 6 months.Conclusions and RelevanceA definition of PASC was developed based on symptoms in a prospective cohort study. As a first step to providing a framework for other investigations, iterative refinement that further incorporates other clinical features is needed to support actionable definitions of PASC.

Hypoxia stimulates pulmonary artery smooth muscle cell (PASMC) proliferation. Recent studies have implicated an important role for microRNAs (miRNAs) in hypoxia-mediated responses in various cellular processes, including cell proliferation. In this study, we investigated the role of microRNA-21 (miR-21) in hypoxia-induced PASMC proliferation and migration. We first demonstrated that miR-21 expression increased by ∼3-fold in human PASMC after 6 h of hypoxia (3% O₂) and remained high (∼2-fold) after 24 h of hypoxia. Knockdown of miR-21 with anti-miR-21 inhibitors significantly reduced hypoxia-induced cell proliferation, whereas miR-21 overexpression in normoxia enhanced cell proliferation. We also found that miR-21 is essential for hypoxia-induced cell migration. Protein expression of miR-21 target genes, specifically programmed cell death protein 4 (PDCD4), Sprouty 2 (SPRY2), and peroxisome proliferator-activated receptor-α (PPARα), was decreased in hypoxia and in PASMC overexpressing miR-21 in normoxia and increased in hypoxic cells in which miR-21 was knocked down. In addition, PPARα 3'-untranslated region (UTR) luciferase-based reporter gene assays demonstrated that PPARα is a direct target of miR-21. Taken together, our findings indicate that miR-21 plays a significant role in hypoxia-induced pulmonary vascular smooth muscle cell proliferation and migration by regulating multiple gene targets.

Nonmuscle myosin light-chain kinase (MYLK) mediates increased lung vascular endothelial permeability in lipopolysaccharideinduced lung inflammatory injury, the chief cause of the acute respiratory distress syndrome. In a lung injury model, we demonstrate here that MYLK was also essential for neutrophil transmigration, but that this function was mostly independent of myosin II regulatory light chain, the only known substrate of MYLK. Instead, MYLK in neutrophils was required for the recruitment and activation of the tyrosine kinase Pyk2, which mediated full activation of β 2 integrins. Our results demonstrate that MYLK-mediated activation of β 2 integrins through Pyk2 links β 2 integrin signaling to the actin motile machinery of neutrophils.Neutrophils are the first line of defense against invading micro-pathogens. To kill pathogens, neutrophils must first attach to the blood vessel wall, then transmigrate into tissue to reach the site of infection and consume pathogens by phagocytosis 1 . Therefore, pathogen-induced adhesion and migration of neutrophils are critical events in the innate immune response 2,3 . In contrast, inappropriate sequestration of neutrophils in tissue coupled with their activation can also cause profound injury, such as that in sepsis-induced acute respiratory distress syndrome 4,5 .Myosin light-chain kinase (MYLK; A000026) is a calcium-calmodulin-dependent kinase that phosphorylates myosin II regulatory light chain (MLC), the substrate for MYLK 6,7 . MYLK has two isoforms: smooth muscle (short form; 108-130 kilodaltons) and nonmuscle (long form; 210 kilodaltons) 8,9 . Mice deficient in nonmuscle MYLK (Mylk −/− mice) are protected from endotoxin-induced lung injury and also have much better survival 10 . The protection in Mylk −/− mice may result from inhibition of the endothelial hyper-permeability response and impaired neutrophil transmigration and activation due to the loss of nonmuscle MYLK function. Nonmuscle MYLK has been shown to be pivotal in endothelial barrier disruption through the regulation of actomyosin contractility in endothelial cells 11,12 . However, the Reprints and permissions information is available online at